This invention relates to a method for controlling the quantity of air flowing into an internal combustion engine, and more particularly, to an adaptive learning control method for regulating engine intake air flow to achieve a scheduled air-fuel ratio.
Recently, fuel based control systems have been applied to fuel injected internal combustion engines to regulate the combustion air-fuel ratio. In such systems, the amount of fuel supplied to each cylinder during an engine cycle is determined directly as a function of the operator demand for engine output, such as indicated by the degree of depression of an accelerator pedal. In response to the amount of injected fuel, the engine intake air flow is then controlled with a closed-loop feedback system to effectuate engine operation at a scheduled air-fuel ratio. Traditionally, a proportional-integral (PI) feedback control scheme has been used to adjust the position the engine intake air throttle valve based upon the difference between the actual mass of air inducted into each engine cylinder and a desired mass of air corresponding to the schedule air-fuel ratio.
This form of closed-loop air control provides relatively accurate air-fuel regulation under constant or slowly varying engine operating conditions. However, when the engine operating conditions change rapidly, the accuracy of the air flow control is limited by air and/or fuel transport time delays inherent in the engine. As a consequence, the conventional closed-loop control system is not capable of accurately tracking and correcting engine air flow during these abrupt transitions. As a result, the actual engine air-fuel ratio can deviate significantly from the scheduled air-fuel ratio, thereby increasing the level of undesirable exhaust emission produced by the engine.